1. Field of the Invention
The present invention relates to a decentering adjustment method for a lens which is used in optical instruments such as a photographic camera, an electronic still camera, a video camera, a projector, a photographic printer and the like, and to a lens device capable for decentering adjustment of a lens.
2. Background Arts
As a lens device for an optical instrument, a zoom lens device is extensively employed. The zoom lens device is constructed of plural lens groups, each of which is held by a lens holding frame. It is at the attachment of the lens group to the lens holding frame that each lens is alligned to accurately come into a refference optical axis and to keep a predetermind interval with each other.
Japanese Patent Laid-Open Publication No. 2000-275494 discloses a lens device with a slidable lens holding frame which moves along a guide shaft provided inside a lens barrel. This type of lens device requires precision in assembling so that the lens group may slide accurately and smoothly in a direction of the optical axis.
In reality, no matter how precise the manufacture of each components such as the lens barrel, the lens holding frame and the guide shaft may be, slight gaps among the components will accumulate in assembling to cause a backlash. Thus, the lens group turns to alter its decentering amount (that is, how deviate from the optical axis of a lens system) when it moves for zooming or focusing, and that could trigger such disadvantages as reduced resolving power, out of focus and so on.
Conventionally, the decentering amount is adjusted as follows. The guide shaft is mounted on the lens holding frame and threadably fixed to the lens barrel, then the relative position of the optical axis of the lens (the center of the lens) to that of the lens system is observed. In case of the deviation, a screw on the guide shaft is loosen to modify the lens position and tighten up again.
However, the above method ends up with retightening the screw many times so that the adjustment operation takes long time and lowers the working efficiency.